1. Field of the Invention
The preset invention relates to a system for monitoring an operating condition of a control rod drive mechanism for use with a PWR (Pressurized Water Reactor).
2. Description of the Prior Art
A typical arrangement of a conventional PWR is that a plurality (generally, 33.about.57 units) of control rod drive mechanisms (hereinafter referred to as CRDMs) 1 . . . are, as depicted in FIG. 8, disposed erectly on an head closure 2 of a reactor vessel in accordance with a rated output of the reactor. Each CRDM 1 is, as illustrated in FIG. 9, composed of a pressure housing mounted on and extending upwardly from the reactor vessel head closure 2, a control rod drive shaft 4 so disposed in the pressure housing 3 as to be movable in a vertical direction, and electromagnetically motive latch mechanisms 5a, 5b and 5c for driving the control rod drive shaft 4 in the up-and-down direction. The electromagnetically motive latch mechanisms 5a, 5b and 5c are intermittently driven by turning ON/OFF a lift coil 6, a coil 7 for a movable gripper and a coil 8 for a stationary gripper in a given sequence which are incorporated in the pressure housing 3, thereby controlling the reactor output by ascending or descending the control rod drive shafts 4. One example of a typical construction of the CRDM is disclosed as a "Linear Motion Device" in Japanese Utility Model Publication No. 35912/1982.
Turning to FIG. 11, there is illustrated the principal portion of the CRDM, i.e., the linear motion device disclosed in the same Utility Model Publication. The CRDM acts to pull out and insert a control rod by gripping a groove chased in the drive shaft 4 connected to the upper part of the control rod. The operation of such a control rod involves the steps of moving up and down a movable magnetic pole 102 referred to as a plunger, and grasping and releasing a latch 103 with a link mechanism. The up-and-down movement of the plunger 102 can be effected by generating magnetic forces while energizing electromagnetic coils 6, 7 and 8 provided on the outer periphery thereof.
In the PWR equipped with the plurality of CRDMs 1 . . . , it is required to constantly monitor whether each CRDM 1 is normally operated or not.
Based on the prior art, a method of monitoring the operating condition of the CRDM 1 comprises the steps of, as illustrated in FIG. 10, mounting a small-sized microphone 9 on the top of the housing 3, detecting sounds emitted when electromagnetically motive latch mechanisms 5a, 5b and 5c depicted in FIG. 9 perform their latch operations by use of the microphone 9, and recording the operating sounds on an unillustrated oscillograph.
There arise, however, the following problems inherent in this method:
(1) The method is not available at high temperatures because of detecting the operating sounds of the electromagnetically motive latch mechanisms 5a, 5b and 5c by use of the microphone 9; and PA1 (2) The microphone has such a characteristic as to detect the operating sounds of the adjacent CRDMs, and it is therefore difficult to discriminate the operating sound of the aiming CRDM with the aid of the output of the microphone 9. Especially when the plurality of contiguous CRDMs are operated at the same moment, the electromagnetically motive latch mechanisms 5a, 5b and 5c of each CRDM function with a slight time-difference, and hence the operating sounds recorded on the oscillograph assume consecutively varying waveforms. As a result, it is almost impossible to discriminate the aiming CRDM on the basis of the waveforms recorded on the oscillograph.
The up-and-down movement, illustrated in FIG. 11, of the plunger 102 can be effected by generating the magnetic forces while energizing the electromagnetic coils 6, 7 and 8 attached to the outer periphery thereof. Electric currents flowing through the electromagnetic coils 6, 7 and 8 at this time contain counter electromotive current components corresponding to the operation of the plunger 102. For this reason, an operating condition of the plunger 102 can be detected indirectly by analyzing the operating sound of the plunger 102 which comes into operation in combination with characteristics of coil currents.
Heretofore, the plunger operating condition is also analyzed by utilizing the above-mentioned principle. In this case, as a time for which the CRDM is operated is as high as 780 msec per step, the waveforms of the coil currents and of the operating sound are once inputted to and recorded on the oscillograph, and thereafter the characteristics of the coil current and of the operating sound are analyzed by human operations.
The number of steps required for a stroke of the CRDM, viz., every pull-out and insertion, is given by 228.times.2=456. For instance, in a pressurized water reactor plant of a 4-loop primary cooling system, where 53 units of CRDMs are prepared, it is required that the data analysis be performed 24168 times, given by 456.times.53, for effecting the analysis of all the steps with respect to the entire CRDMs. The human-operation-based analysis needs approximately 20 minutes per step, and hence a large amount of time and also a good number of workers are required for the foregoing number of data analyzing operations. Besides, the analyzing process has no alternative but to depend on the human operations, so that it is impossible to steer clear of an artificial fault. This may inevitably become a factor for causing a mistake in judgement when making a systematic evaluation.